Developments in methods of manufacturing very small devices, such as microelectronic devices, have made it possible to precisely and reproducibly make devices having features with nanometer-scale dimensions. Apart from use of such methods in microelectronic device production, similar technology has been used to make devices for handling biological materials, such as cells and macromolecules.
Microengineered bio-handling devices having structural elements with minimal dimensions ranging from tens of micrometers (the dimensions of biological cells) to nanometers (the dimensions of some biological macromolecules) have been described. This range of dimensions (nanometers to tens of micrometers) is referred to herein as “microscale.” For example, U.S. Pat. No. 5,928,880, U.S. Pat. No. 5,866,345, U.S. Pat. No. 5,744,366, U.S. Pat. No. 5,486,135, and U.S. Pat. No. 5,427,946 describe microscale devices for handling cells and biological molecules.
Hemocytometry is a field of medical analysis and research wherein blood cells are analyzed using variety of techniques and devices. Basic manually-operated devices such as microscope slides with Neubauer or Makler chambers were developed over a century ago. These devices are expensive, reusable, and lack flexibility, multiple features, and disposability. Disposability is especially desirable to minimize medical personnel interaction with potentially hazardous biological specimens.
Every year, approximately 500,000 patients are diagnosed with blood disorders worldwide, including about 30,000 per year in the United States. Many blood disorders can be alleviated by transplantation of stem cells (i.e., relatively non-differentiated cells which retain at least hematopoietic capacity) into the patient. The ideal source of stem cells is the same patient to whom the cells are to be administered. However, hematopoietic (and other) stem cells are relatively rare in adults, and can be difficult to isolate in large numbers.
Blood drawn from the umbilicus shortly after delivery (“cord blood”) is a rich source of hematopoietic stern cells. Cord blood storage methods are presently known and used commercially, but have the drawback that a relatively large volume (e.g., 100 to 250 milliliters) of blood must be stored in order to preserve a sufficient number of hematopoietic stem cells for use in future medical procedures. The large volume of cord blood that is stored increases the cost and decreases the convenience of the procedure. The stored volume could be decreased significantly (e.g., to 0.1 to 1 milliliter) if stem cells could be separated from cord blood prior to storage. However, present methods of separating stem cells from cord blood are expensive and cumbersome and are sometimes ineffective. The present invention overcomes the shortcomings of previously known stem cell separation methods and facilitates efficient and cost-effective separation of stem cells from cord blood.